The present invention relates to a power switch assembly for an electric tool such as a hand electric tool which is driven by a DC motor, and particularly relates to such a power switch assembly which is provided with a convenient means of reversing operation. Even more particularly, the present invention relates to such a power switch assembly, which particularly is provided with a means for properly sealing a switch lever structure which extends from its inside to its outside.
In the prior art, there have been proposed various types of electrically driven power tools such as electric screw drivers, electric power drills, electric saws, and the like. Such electric power tools have typically been powered by DC motors, and very often have been endowed with the function of selective reversibility, i.e. with the function that the rotational direction of an electric motor incorporated in the tool can be selectively reversed, at the discretion and at the behest of the user of the power tool. And various power switch assemblies have been proposed for such electric power tools, incorporating such a function of selective reversability. Also, the function of selectively variable controllability with regard to speed has been proposed; for example in Japanese Patent Laying Open Publication Serial No. 60-160918 (1985) which it is not hereby intended to admit as prior art to the present patent application except to the extent in any case mandated by applicable law, there is disclosed a type of switch for an electric power tool, in which the rotational speed of such an electric motor incorporated in the tool can be altered, i.e. which is endowed with a speed control unit which provides the function that the rotational speed of said electric motor can be selectably varied from slow through medium to fast, again at the discretion and at the behest of the user of the power tool.
However, this type of power switch assembly is subject to a number of problems.
First, since typically space is at a premium in such a construction, it is difficult to incorporate a reversing mechanism for such a power switch assembly in the same restricted compass as a speed control mechanism thereof. Accordingly, conventionally, the reversing mechanism has been typically incorporated in the grip of such an electric power tool, i.e. in a position remote from the speed control mechanism. Such a place, although necessitated for reasons of limited space availability, has been very inconvenient for operation of the power tool, and has often necessitated that the user of the power tool is required to use both hands, for performing certain control actions with respect to the power tool. This is most inconvenient and makes handling of the power tool more difficult.
Further, as such a speed control mechanism for such a power switch assembly for a power tool, it has been typical to utilize a slide type switch, which controls both the ON/OFF action for the motor of the power tool and the torque supplied by said motor, by being slid by the motion of a rocking lever or the like which extends from the interior of the power switch assembly to the outside thereof. However, since this construction requires an opening to be provided in the casing of the power switch assembly for accommodating the stroke of the rocking lever or the like, and since such an opening presents an opportunity for dust or dirt or the like to enter from the outside into the interior of the power switch assembly, which might inevitably engender poor functioning such as poor contact performance of the power switch assembly, therefore a special type of sealing arrangement for such an opening, such as a rubber bellows or the like, is inevitably required for accommodating the inevitably relatively large stroke of motion of such a lever. The relatively high cost of such a special type of sealing arrangement has been a major obstacle in the reduction of the overall cost of such a power switch assembly for such a power tool.